Developing apparatus having improved developer distribution

Abstract

The present invention is to provide a developing apparatus having a supply screw and a recovery screw both of which are arranged vertically to circulate developer, wherein a component in a normal direction of pressure generated by the recovery screw is made larger than that of pressure generated by the supply screw. Thereby, lowering and raising of developer is suppressed and occurrence of fog on the image and the smoke of toner are prevented. Alternatively, a radial member and a centrifugal member are applied to the supply screw and the recovery screw, respectively. Thereby, developer is prevented from moving between screws in the midst of the transportation. Still alternatively, a preliminary stirring portion is provided on extension of a stirring screw at upperstream side. The preliminary stirring portion has a cylindrical body with inlets and outlets. Both inside and outside of the cylindrical body, screws are provided and inclines of screw blades are reversed to each other. Thereby, it enables the developing apparatus to transport the developer which is sufficiently stirred and charged to a development zone without being accompanied by a large-scaled apparatus.

What is claimed is: 
     
       1. A developing apparatus to develop a latent image with developer including: a first screw for transporting developer in an axial direction;   a second screw arranged above the first screw and for transporting developer in an axial direction; and   means for generating a first component in a normal direction of pressure by rotation of the first screw and for generating a second component in a normal direction of pressure by rotation of the second screw, the first component being larger than the second component.   
     
     
       2. A developing apparatus according to claim 1, wherein rotational speed of the first screw is made faster than that of the second screw. 
     
     
       3. A developing apparatus according to claim 1, wherein the first screw has a pitch smaller than that of the second screw. 
     
     
       4. A developing apparatus according to claim 1, wherein the first screw includes more threads per unit length than the second screw. 
     
     
       5. A developing apparatus according to claim 1, wherein a paddle is provided on the first screw and no paddle is provided on the second screw. 
     
     
       6. A developing apparatus according to claim 1, wherein the first screw has a paddle having an area larger than an area of a paddle on the second screw. 
     
     
       7. A developing apparatus to develop latent image with developer including: a development roller;   a first screw for, while transporting developer in an axial direction, supplying the developer to the development roller;   a second screw arranged below the first screw for recovering developer from the development roller to transport it in an axial direction;   a third screw arranged above the first screw and for transporting developer in an axial direction; and   means for generating a first component in a normal direction of pressure by rotation of the first screw and for generating second and third components in a normal direction of pressure by rotation of the second and third screws respectively, the first component being larger than the second and third components.   
     
     
       8. A developing apparatus according to claim 7, wherein rotational speed of the first screw is made faster than that of other screws. 
     
     
       9. A developing apparatus according to claim 7, wherein the first screw has a pitch smaller than that of other screws. 
     
     
       10. A developing apparatus according to claim 7, wherein the first screw includes more threads per unit length than the other screws. 
     
     
       11. A developing apparatus according to claim 7, wherein a paddle is provided on the first screw and no paddle is provided on other screws. 
     
     
       12. A developing apparatus according to claim 7, wherein the first screw includes paddles, and at least one of the second and third screws includes paddles and an area of each of the paddles of the first screw is larger than areas of each of the paddles of the other screws. 
     
     
       13. A developer transporting screw which rotates about an axis to transport developer in an axial direction has a shaft and a screw blade projecting from the shaft and radial means for applying an inward pressure on the developer by centripetal force, the radial means projecting from the shaft and located between turns of the screw blade. 
     
     
       14. A developer transporting screw according to claim 13, wherein the radial means is a blade member including a generally concave front surface with respect to a direction of rotation of the developer transporting screw. 
     
     
       15. A developer transporting screw which rotates about an axis to transport developer in an axial direction has a shaft and a screw blade projecting from the shaft and a blade member including a generally convex front surface with respect to a direction of rotation of the developer transporting screw for applying an outward pressure on the developer by centrifugal force, the blade member projecting from the shaft and located between turns of the screw blade. 
     
     
       16. A developing apparatus including: a development roller;   a plurality of developer transporting screws each rotating about an axis to transport developer in an axial direction and each having a shaft and a screw blade projecting from the shaft; and   radial means arranged in an area of one of the developer transporting screws where developer is delivered from other developer transporting screws and applying an inward pressure on the developer by centripetal force, the radial means projecting from the shaft of the one developer transporting screws and located between turns of the screw blade of the one developer transporting screws.   
     
     
       17. A developing apparatus according to claim 16, wherein the radial means is a blade member including a generally concave front surface with respect to a direction of rotation of the one of the developer transporting screws. 
     
     
       18. A developing apparatus including: a development roller;   a plurality of developer transporting screws rotating about an axis to transport developer in an axial direction and each having a shaft and a screw blade projecting from the shaft; and   a blade member including a generally convex front surface with respect to the direction of rotation of the developer transporting screws, the blade member arranged in an area of one of the developer transporting screws where developer is delivered to other developer transporting screws and applying an outward pressure on the developer by centrifugal force, the blade member projecting from the shaft of the one of the developer transporting screws and located between turns of the screw blade of the one of the developer transporting screws.   
     
     
       19. A developing apparatus including: a development roller;   a plurality of developer transporting screws rotating about an axis to transport developer in an axial direction and each having a shaft and a screw blade projecting from the shaft; and   radial means arranged in an area where developer is recovered from the development roller by one of the developer transporting screws and applying an inward pressure on the developer by centripetal force, the radial means projecting from the shaft of the one of the developer transporting screws and located between turns of the screw blade of the one of the developer transporting screws.   
     
     
       20. A developing apparatus according to claim 19, wherein the radial means is a blade member including a generally concave front surface with respect to a direction of rotation of the one of the developer transporting screws. 
     
     
       21. A developing apparatus including: a development roller;   a plurality of developer transporting screws rotating about an axis to transport developer in an axial direction and each having a screw blade wrapped around a shaft: and a blade member including a generally concave front surface with respect to a direction of rotation of the developer transporting screw, the blade member arranged in an area where developer is supplied to the development roller by one of the developer transporting screws and applying an outward pressure on the developer by centrifugal force, the blade member projecting from the shaft of the one of the developer transporting screws and located between turns of the screw blade of the one of the developer transporting screws.   
     
     
       22. A developing device which circulates and supplies developer to a developer carrier including: a developer storage tank;   a plurality of transporting screws for transporting developer in an axial direction within the developer storage tank; and   a preliminary stirring means for stirring developer, the preliminary stirring means having a cylindrical body provided inside the developer storage tank, an internal screw provided inside the cylindrical body and rotatable about an axis, and an external screw provided outside the cylindrical body and rotatable about the axis;   wherein a first transporting direction of developer by the internal screw and a second transporting direction of developer by the external screw are reversed with respect to each other.   
     
     
       23. A developing apparatus according to claim 22, wherein the preliminary stirring means is arranged on an extension of one of the transporting screws and the transporting direction of the internal screw is coincided with the transporting direction of the one transporting screw. 
     
     
       24. A developing apparatus according to claim 23, wherein the cylindrical body is formed with a passage hole through which internal and external developers can pass;   one end of the cylindrical body is positioned within a development zone; and   the other end of the cylindrical body and the passage hole are positioned outside the development zone.   
     
     
       25. A developing apparatus according to claim 23, wherein the plurality of the transporting screws are arranged vertically. 
     
     
       26. A developing apparatus according to claim 24, wherein the plurality of the transporting screws are arranged vertically. 
     
     
       27. A developing apparatus according to claim 24, wherein the developer storage tank is formed with a replenishing port for replenishing developer so that developer replenished from the replenishing port flows into the cylindrical body. 
     
     
       28. A developing apparatus according to claim 26, wherein the developer storage tank is formed with a replenishing port for replenishing developer so that developer replenished from the replenishing port flows into the cylindrical body. 
     
     
       29. A developing apparatus according to claim 22, wherein the cylindrical body is formed with a passage hole through which internal and external developers can pass;   one end of the cylindrical body is positioned within a development zone; and   the other end of the cylindrical body and the passage hole are positioned outside the development zone.   
     
     
       30. A developing apparatus according to claim 29, wherein the plurality of the transporting screws are arranged vertically. 
     
     
       31. A developing apparatus according to claim 29, wherein the developer storage tank is formed with a replenishing port for replenishing developer so that developer replenished from the replenishing port flows into the cylindrical body. 
     
     
       32. A developing apparatus according to claim 30, wherein the developer storage tank is formed with a replenishing port for replenishing developer so that developer replenished from the replenishing port flows into the cylindrical body. 
     
     
       33. A developing apparatus according to claim 22, wherein the plurality of the transporting screws are arranged vertically.